<!DOCTYPE html>
<html>
<head>
    <title>Simple Calculator</title>
    <meta charset="utf-8" />
</head>
<body>
    <section>
        <table border="1">
            <tr>
                <th colspan="4">
                    <input type="text" contenteditable="true" value="123" />
                </th>
            </tr>
            <tr>
                <td>
                    <input type="button" value="1" />
                </td>
                <td>
                    <input type="button" value="2" />
                </td>
                <td>
                    <input type="button" value="3" />
                </td>
                <td>
                    <input type="button" value="+" />
                </td>
            </tr>
            <tr>
                <td>
                    <input type="button" value="4" />
                </td>
                <td>
                    <input type="button" value="5" />
                </td>
                <td>
                    <input type="button" value="6" />
                </td>
                <td>
                    <input type="button" value="-" />
                </td>
            </tr>
            <tr>
                <td>
                    <input type="button" value="7" />
                </td>
                <td>
                    <input type="button" value="8" />
                </td>
                <td>
                    <input type="button" value="9" />
                </td>
                <td>
                    <input type="button" value="*" />
                </td>
            </tr>
            <tr>
                <td colspan="2">
                    <input type="button" value="0" style="width:68px" />
                </td>
                <td>
                    <input type="button" value="." />
                </td>
                <td>
                    <input type="button" value="/" />
                </td>
            </tr>
        </table>
    </section>
</body>
</html>